Conventional two-dimensional cultures of cancer cells are widely used for evaluating potential anti-cancer drugs. However, growing evidence shows that cancer cells respond differently to anticancer drugs in a two-dimensional monolayer culture than they would in vivo, where cells reside in a three-dimensional environment. To more accurately model the effects of potential drugs in vivo a three dimensional aggregate of cells, or cellular spheroid, is desired. Presently, the hanging drop method is used to produce cancer cell spheroids for anti-cancer drug screening. The hanging drop method, which produces spheroids by suspending cells in droplets of medium, suffers from several shortcomings. For instance, surface tension limits the maximum size of a drop prepared by the hanging drop method, also, due to the small size of the suspended drops, evaporation is a large concern. As the water within the drop evaporates, the concentration of soluble components such as proteins and salts in the medium increases, subjecting the cells to a changing osmotic pressure, thus compromising their normal morphology and function. The media also needs to be refreshed daily to avoid the build up of cell waste and because of the small volume of media available to the cells. The exchange of media is generally done by hand, using a pipette, increasing the likelihood of incorporating errors such as aspirating out spheroids from hanging drops or introducing shear stress to cells due to manual pipetting. In addition, treating spheroids with exact drug concentrations is a challenge due to the presence of existing media. The hanging drop method is also sensitive to physical movements that can result in the detachment of drops and the spheroids within from the surface from which the drops hang.
Presently, a need exists for methods of screening drug compounds in three-dimensional cultures that do not suffer from the above problems, and thus enable reliable, high throughput screening of potential drug compounds.